For many years, the subject matter encompassed by the title of this book was largely limited to those who were interested in the two most economically important organic materials found buried in the Earth, namely, coal and petroleum. The point of view of any discussions which might occur, either in scientific meetings or in books that have been written, was, therefore, dominated largely by these interests. A great change has occurred in the last decade. This change had as its prime mover our growing knowledge of the molecular architecture of biological systems which, in turn, gave rise to a more legitimate asking of the question: "How did life come to be on the surface of the Earth?" A second motivation arose when the possibilities for the exploration of planets other than the Earth-the moon, Mars, and other parts of the solar system-became a reality. Thus the question of the possible existence of life elsewhere than on Earth conceivably could be answered.

In 1936 a German chemist identified certain organic molecules that he had extracted from ancient rocks and oils as the fossil remains of chlorophyll--presumably from plants that had lived and died millions of years in the past. It was another twenty-five years before this insight was developed and the term "biomarker" coined to describe fossil molecules whose molecular structures could reveal the presence of otherwise elusive organisms and processes.
Echoes of Life is the story of these molecules and how they are illuminating the history of the earth and its life. It is also the story of how a few maverick organic chemists and geologists defied the dictates of their disciplines and--at a time when the natural sciences were fragmenting into ever-more-specialized sub-disciplines--reunited chemistry, biology and geology in a common endeavor. The rare combination of rigorous science and literary style--woven into a historic narrative that moves naturally from the simple to the complex--make Echoes of Life a book to be read for pleasure and contemplation, as well as education.